Rooted in the expression: "Hung like a horse", a Unicorn Dick or UD, refers to a exceptionally large penis with the magical powers of a Unicorn. These powers include: making women sneak out of bed with men they are dating in order to pursue the UD, making women jump from man to man looking to fill a void that only a UD can fill, and making women lie straight faced to a man they allegedly care about when confronted about sneaking out to pursue the UD.

I don't understand why she is with him, he has no job, he treats her like shit, and he spends all her money.